Diamond Hell

Cut the one off your current downpipe and weld to your replacement manifold and downpipes.

Done.

You must disconnect the lambda to see what difference it makes.

Until you've done that you're going to be groping around in the dark.

I think there are two different issues here:

1. The exhaust was changed

2. The car ran out of fuel.

1. caused no issues.

2. may have caused the motor to run lean, destroying the lambda through overheating and getting beaten up with mis-fires etc as the car ran out of fuel.

How does the car run if the lambda's disconnected?